Due to the increasing government regulation of vehicle emissions, exhaust sensors have been employed to ensure that a vehicle is within emissions standards. To this end, most current gasoline vehicles in the United States incorporate one or more exhaust gas oxygen sensors (EGO). Basically, typical exhaust gas oxygen sensors provide either voltage or current signals dependent on the oxygen concentration in an exhaust stream, with the signals being used as feedback to adjust an operating air/fuel ratio. Furthermore, many diesel vehicle manufacturers and sensor suppliers have begun development toward sensors for nitrogen oxides (NOx), hydrocarbon (HC) and soot in engine exhaust, as well as ammonia (NH3).
Prior to use, an exhaust gas sensor needs to be calibrated. For example, to calibrate an oxygen sensor, a calibration gas containing a mixture of oxygen and other gases having a known concentration of oxygen is applied to the sensor. The measured value of oxygen is compared to the known concentration of oxygen in the calibration gas and a correction factor is calculated. Over time, the sensitivity of an exhaust gas sensor can drift, at least in part because the sensor is exposed to extreme temperatures, debris and water from the exhaust. That is, these sensors are subjected to damage during operation of the vehicle because debris from the exhaust and accumulating soot over time can alter the signal outputs of the sensor. Therefore, to remain accurate, the exhaust gas sensor may require periodic calibration.
To address the above, it would be extremely beneficial to incorporate a self-calibrating sensor system into a vehicle to enable periodic self-calibration of an exhaust gas sensor. More specifically, it would be desirable to employ components already in the vehicle to periodically provide a calibration gas having a known gas concentration to the exhaust gas sensor to test the exhaust gas sensor and make any necessary adjustments to a correction factor established for the sensor. It would be particularly advantageous to provide a system that would enable calibration of an exhaust gas sensor while an engine of the vehicle is running. Finally, it would be desirable to provide protection of the sensor from debris, water and accumulating soot.